Nature won't reforest uplands by itself, experiment suggests

"Rewilding" upland areas can take decades without the intervention of land managers, an experiment in the southern Scottish Highlands has shown.

Image: Doug Lee (CC BY-SA 2.0)
Image: Doug Lee (CC BY-SA 2.0)

The experiment, the first of its kind in Scotland, was set up at at Glen Finglas in upper Perthshire in 2002 to explore how changes in farming policy, particularly declining livestock numbers, might affect upland biodiversity.

It assessed the impact of intensification (tripling sheep numbers), abandonment (removing sheep) and grazer diversification (partial replacement of sheep by cattle) on vegetation and hence on other wildlife, an took in a mixture of uplands habitats, namely wet heath, wet and dry grassland and sedge mire.

Professor Robin Pakeman, of the James Hutton Institute, part of the research team, said: "The responses of individual plant species to the experiment took a minimum of 12 years and often 15 years to become apparent, with some species showing no detectable changes."

The research is intended to inform rewilding projects, in which aim to encourage natural processes to regenerate the landscape, including by introducing missing species.

The results showed that:

  • Tree invasion was minimal, apart from one ungrazed plot near a wooded ravine;
  • Productive grasslands, such as those dominated by bents and fescues, contain few species capable of responding to reduced grazing, so the response to grazing removal was minimal;
  • less productive mire communities contained species capable of increasing after grazing removal;
  • Partial replacement of sheep by cattle had little impact on the vegetation apart from suppressing bracken and blaeberry;
  • Increased grazing actually increased species diversity.

The experiment suggests that without the direct involvement of land managers, vegetation change in these relatively infertile grasslands is extremely slow.

The results are published in the British Ecological Society's Journal of Applied Ecology.

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